Combustion and flame detecting



Nov. 5, 1957 c. D. M cRAcKEN COMBUSTION AND FLAME DETECTING APPARATUSFiled April 30, 1954 INVENTOR. CALvm D. MAQLRMKEN ATTORNEY.

United States Patent COMBUSTION AND FLAME DETECTING APPARATUS Calvin D.MacCracken, Tenafly, N. 1., assignor to Jet- Heet, Inc., Englewood, N.J., a corporation of New York Application April 30, 1954, Serial No.426,860

1 Claim. (Cl. 15828) This invention relates to improvements incombustion devices having flame detecting apparatus, and particularly toflame detecting apparatus of the so-called flame electrode type.

This application is, in part, a continuation of my copending applicationSerial No. 145,531, filed February 21, 1950, now Patent No. 2,705,530,granted April 5, 1955.

As is well known, ionization of the heated air in a flame or the likemakes it possible to pass a rectified electric current through the flamebetween a pair of electrodes contacted by the flame. In combustionapparatus, this phenomenon has been used for flame detection by mountingan electrode to project into the path of current between the electrodeand the chamber wall and through the associated electric circuit isutilized as a control means for maintaining the supply of fuel to theburner. If the flame should be extinguished for any reason, theresulting interruption in electric current flow will cause the controlcircuit to react in such a fashion as to shut off the supply of fuel.

One of the problems that has been encountered with flame detectingapparatus of this type, especially when operating in an oil flame, isthe tendency for carbon to collect on the detecting electrode. After asuflicient period of time, enough carbon may build up to bridge thespace between the electrode and its companion element in the electriccircuit so that current flows continuously whether or not there is aflame in the area. If the electrode is located in a part of the flamethat is hot enough to prevent carbon formation, the temperature is sohigh that the electrodeis liable to be burned off.

It is, accordingly, among the objects of the present invention toprovide an improved combustion device having flame detecting apparatusof the flame electrode type wherein the formation of carbon deposits onthe electrode are avoided and yet the electrode is adequately protectedagainst deterioration due to overheating.

In accordance with a preferred embodiment of the invention, theforegoing and other related objects and advantages are obtained in aflame producing and detecting apparatus wherein the flame electrode ismounted in a part of a combustion chamber that is lined with refractorymaterial. The refractory material becomes heated sufiiciently to burnoff any carbon on the electrode by radiant heat. In order to preventoverheating, an air space is provided around the flame detectingelectrode mounting where the latter passes through the refractory inorder to allow cooling air to flow over the electrode.

A more complete understanding of the invention can be had by referenceto the following description of illustrative embodiments thereof, whenconsidered in connection with the accompanying drawing, the singlefigure of which is a section view of a burner apparatus having a flamedetector embodying the invention.

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Referring to the drawing, the fuel burner there illustrated comprises anoil burner provided with a liquid fuel nozzle or atomizer 10 of thereturn-flow type having a supply pipe 12 and a return pipe 14. Theatomizer 10 supplies fuel oil in the form of a fine cone-shaped spray.The fuel burner further comprises a pair of cylindrical sleeves 16, 18disposed one within the other and held in spaced coaxial relation by acircular, dished-shaped end wall 20 having its outer portion formed intoa circular channel 22 which cooperates with the edges of the sleeves 16,18 and is secured thereto in any suitable way. The end wall 20 isprovided at its center with an opening 24 through which the fuel sprayfrom the atomizer enters the combustion space defined by the innersleeve 16. Mounted on the end wall 20 is a casing 26 which houses theatomizer.

The inner sleeve 16 of the fuel burner is perforated with a large numberof small holes 28, and is also provided with several series ofcircularly arranged larger holes 30. The purpose of the small holes 28is to permit air to seep through the inner sleeve 16, thereby providingon its inside surface a layer or cushion of air for the purpose ofpreventing carbon formation, as is explained in applicants copendingapplication Serial No. 277,185, filed March 18, 1952, now Patent No.2,692,014, granted October 19, 1954. The larger holes 30 in the innersleeve admit freely not only the air necessary to support substantiallycomplete combustion of the liquid fuel, but also additional air whichdilutes the gaseous products of combustion. An ignition device 32 of anywell known form is shown as extending through aligned openings in thesleeve 16, 18 into the combustion space within the inner sleeve.

The combustion space defined by the inner sleeve 16 is extended by acylindrical sleeve 34 of refractory material. The sleeve 34 isfabricated of refractory cement and'may be molded for additionalstrength on a wire mesh 36 inside a casing 38. The outer diameter of therefractory sleeve 34 is substantially the same as the diameter of theouter sleeve 18, while the inner diameter of the sleeve 36 is slightlygreater than that of the inner sleeve 16. The refractory terminates ashort distance from the end of the inner sleeve 16, with the gap betweeninner sleeve 16 and the refractory sleeve 34 being bridged by a metalcollar 40 provided by a reduced diameter portion of the casing 38. Thecollar 40 has the same diameter as the inside diameter of the refractorysleeve, and overlaps the end of the inner sleeve 16. The sleeve 38 isheld in place by struck-out portions 42 of the collar 40 which engagethe inner sleeve 16, thereby maintaining the collar and the sleeve inaccurate coaxial alignment with a small annular space 44 between sleeveand collar.

The fuel burner is located within a casing 46 to which air is suppliedunder pressure through an inlet 48 from a blower (not shown). This airenters the annular space 50 between the inner and outer sleeves, asindicated by the arrow a. The major portion of the air enters thecombustion chamber through the opening 30 in the inner sleeve, whilesome of the air seeps through the smaller openings 28. By passingthrough'the annular space 50 between the sleeves 16, 18, the air absorbsheat from the inner sleeve 16 before passing into the combustionchamber, and also serves to moderate the temperature of the outer sleeve18. The combustion products flow out of the burner through therefractory sleeve 34.

The novel manner in which a flame electrode is mounted in the combustionchamber will now be described. The flame electrode is shown ascomprising a rod 52 of suitable heat-resisting and current-conductingmaterial, such as a compound containing silicon carbide and freesilicon. The rod 52 is'mounted in and projects through a sleeve portion56 from which arms 58 project.

54 f insulating material, such as porcelain. Secured to the porcelainsleeve 54 is a metal spider having a hub These arms 58 are provided withangularly extending ends 60 having perforations through which extendscrews 62 which enter threaded holes in a flange 64 which is secured tothe outer face of the sleeve casing 38 in any suitable manner, as byspot welding. It will be noted that an annular space 66 is providedbetween the porcelain sleeve 54 and the wall of the opening in therefractory lining 34 of the combustion chamber. It will also be notedthat the opening through the flange 64 is of larger diameter than thediameter of the porcelain sleeve 54. Therefore, air is permitted to flowinto the combustion .chamber through the annular space 66, therebycooling the porcelain sleeve 54 which is, of course, subjected toheating by the flaming gases in the combustion chamber. In this way,cracking and sooting of the porcelain sleeve 54 of the flame electrodeis prevented, and the rod 52 of the flame electrode is supported in thepath of the flaming gases. Experience has proved that, when the flame,electrode is thus mounted in the wall of the combustion chamber, theflame electrode functions satisfactorily to permit the passage of arectified electric current (in a control circuit not shown) through therod 52 and the ionized space within the combustion chamber to anyexposed metal part, such as the end of the inner sleeve 16 of the fuelburner. At the same time, the radiant heat of the refractory effectivelyprevents formation of carbon deposits on the porcelain 54 or on theelectrode 52, while the air space provides a cooling air current whichprevents burning of the electrode. Also, the air space allows air toflow past the electrode after the burner is shut down but while theblower is still operating. This blows away any air ionized by therefractory, which ionized air otherwise might pass current and give afalse indication of flame in the combustion chamber.

I claim:

In a combustion and flame detecting apparatus including a liquid fuelburner of the type comprising a housing to which air is supplied underpressure and which encloses a pair of cylindrical sleeves which areclosed at one end and open at the other end, said sleeves being disposedone within the other in spaced coaxial relation, and said burner furtherincluding an atomizing nozzle at said closed end of said sleeves fordischarging atomized liquid fuel into the inner one of said sleeves,said inner sleeve having side openings therein for admitting said airsupply to said housing into'the space inside said inner sleeve, theimprovement which comprises the combination with said burner of anopen-ended sleeve of refractory material extending through a wall ofsaid housing from the open end of said inner sleeve as a continuationthereof, said refractory sleeve having a side opening thereinintermediate the ends thereof and within said housing, a flameelectrode, a sleeve of insulating material enclosing a portion of saidelectrode, said insulating sleeve having smaller cross-sectionaldimensions than the corresponding crosssectional dimensions of saidopening, said insulating sleeve being supported in said opening andspaced from said refractory material, with said electrode extending intothe space inside said refractory sleeve, whereby to expose saidelectrode to radiant heat from the inner surface of said refractorysleeve to prevent the accumulation of carbon deposits from saidelectrode and to provide for the flow of cooling air from said housingthrough the space between said insulating sleeve and said refractorymaterial.

References Cited in the file of this patent UNITED STATES PATENTS1,899,744 Briesky et a1 Feb. 28, 1933 2,173,115 Hutto Sept. 19, 19392,282,551 Yates May 12, 1942, 2,538,952 Yates et al. Jan. 23, 19512,541,236 Giuffrida Feb. 13, 1951 2,698,655 Meredith Jan. 4, 1955

